Science: Physical Science Bohr’s Model Lewis Structure

Science: Physical Science Niels Bohr Gilbert N. Lewis Born in Denmark 20th Century physicist (scientist) Worked on the Manhattan Project during World War II. This is the project that produced the first atomic bomb. Born in the USA 20th Century physicist (scientist) Home-schooled until the age of 13 when he entered the preparatory school of the University of Nebraska.

Science: Physical Science Bohr’s model drawing looks very much like the solar system Helps us understand electron configuration Helps us understand why and how some elements will bond with other elements

Shells: Basics Let's cover some basics of atomic shells: Science: Physical Science Let's cover some basics of atomic shells: The center of the atom is called the nucleus. Electrons are found in areas called shells. c. Shells are areas that surround the center of an atom.  Shells: Basics

Important Things to Remember Science: Physical Science Each shell corresponds to a period on the Periodic Table. You MUST load each shell before you move on to the following one. The number of electrons on each shell can only be up to the number of elements found on the corresponding period. Example: The first shell can only have a maximum of 2 electrons because there are only 2 elements on the first period of the table (Hydrogen and Helium) Bohr’s Model: Step by Step Directions Important Things to Remember

Bohr’s Model: Step by Step Directions Science: Physical Science Locate the element on the Periodic Table and write the information about the element. Draw the nucleus and write the number of protons and neutrons inside the nucleus. Draw the correct amount of shells outside the nucleus based on the row number where the element is found. Start loading electrons on each shell, beginning from the inside and moving to the outside. Bohr’s Model: Step by Step Directions

Science: Physical Science Bohr ‘s Model: Example 1 Element: Helium Atomic #: 2 Atomic Mass: 4.003 Protons: 2 Neutrons = 4 – 2 (Atomic Mass – Protons) Electrons: 2 P= 2 N= 2

Science: Physical Science Bohr ‘s Model: Example 2 Element: Neon Atomic #: 10 Atomic Mass: 20.183 Protons: 10 Neutrons = 20 – 10 (Atomic Mass – Protons) Electrons: 10 (2 on the inner shell / 8 on the outer shell) P= 10 N= 10

Science: Physical Science Octet Rule (Lewis Rule of Eight) When atoms combine to form molecules, they generally each lose, gain, or share valence  electrons until they attain or share eight. Number of valence electrons is the same as number of the group where the element is found (don’t count transition metals). Example: Hydrogen = 1 valence electron, Calcium = 2 valence electrons, Carbon = 4 valence electrons. Lewis Structure Important things to remember

Science: Physical Science For the example we will use HCN Calculate the number of valence electrons that move around it. We have: 1 + 4 + 5 = 10 Add a pair of bonding electrons between every two atoms. H : C : N Add the rest of the electrons to the outer atoms, until they meet the octet rule . Hydrogen is an EXCEPTION. It only needs 2 electrons around it. H C N Lewis Structure Step by Step Directions So far, Nitrogen satisfied the octet rule and we have placed the 10 valence electrons. However, Carbon only has 2 valence electrons. What’s next?

Science: Physical Science Nitrogen will have to share electrons with Carbon. We can move 4 electrons. H C N We now have 8 electrons around each atom and a total of 10 valence electrons. Next, we need to replace each pair of bonding electrons with a simple line to show the bond. H C N Lewis Structure Step by Step Directions

Science: Physical Science Carbon is in Group 4 (if we don’t count the transition metals). Oxygen is in Group 6 (if we don’t count the transition metals). Thus we have: C = 4 valence electrons; O = 6 valence electrons. Multiply 6 x 2 = 12 (remember there are 2 Oxygen atoms in Carbon dioxide. Total = 16. Add a pair of bonding electrons between every 2 atoms. O C O We used 4 electrons out of 16. We need to start placing the other electrons to satisfy the octet rule. Lewis Structure Example using Carbon dioxide - CO2

Science: Physical Science Place electrons around the outer atoms O C O 7) The Oxygen met the octet rule but not the Carbon atom. Each Oxygen shares 2 electrons with the Carbon. 8) Replace the bonding electrons with simple lines. Lewis Structure Example using Carbon dioxide - CO2 – Cont’ O C O C O C O O C O C O O C O C O O C O O C O You are done!